Wells that produce heavy oil from low pressure reservoirs require some form of artificial lift, such as pumping for example, from the bottom of the wellbore to raise the fluids to the surface. These wells may be produced without sand screens or other forms of downhole sand control that would limit the wells' productivity. As a result, wells of this type are prone to produce significant quantities of sand. In many cases, the upward velocity of the production fluids in the wellbore is not sufficient to lift the sand with the fluid production, and a portion of the sand settles to the bottom of the well. Over time, the sand in the bottom of the well covers up the portion of the well that is open to the oil reservoir, effectively blocking the flow of fluids from the reservoir into the wellbore. It may also plug or restrict the flow into the pump. The current method of solving such a problem requires a workover rig, crane and/or a coiled tubing unit to remove the pump and flush the sand out of the well.
Employing liquid pressure for long-range conveyance of materials in bulk is described by U.S. Pat. No. 4,992,006 to Drobadenko et al., incorporated herein by reference. However, the invention of the '006 patent is of particular use in the mining industry, construction, metallurgy and agriculture. It discloses a device for hydraulic conveyance of loose materials with a toroidal chamber having an equatorial plane thereof set with respect to a horizontal plane at an angle dependant on the internal friction of the loose material, when saturated with the liquid used for hydraulic conveyance. The chamber is provided with pipes for charging the loose material and for discharging the liquid, both of the pipes being arranged on one side with respect to the meridianal plane, and a slurry discharge unit arranged on its other side.
U.S. Pat. No. 4,952,099, also to Drobadenko et al., incorporated herein by reference, describes a device for hydraulic conveyance of loose materials with four pipes, one for liquid discharge, the second for loose material charging, the third for feeding the pressure liquid flow and a fourth for slurry discharge in an upward flow. The pipes are held by a hemispherical cover and are arranged coaxially in such a manner that the loose material charging pipe is accommodated inside the liquid discharge pipe, the pressure liquid flow feeding pipe is accommodated inside the loose material charging pipe, and the slurry upward flow discharging pipe is accommodated inside the pressure liquid flow feeding pipe, all of the pipes being arranged coaxially with the longitudinal axis of a housing chamber and having some of their portions located inside the chamber.
U.S. Pat. No. 4,978,251, to Drobadenko et al., incorporated herein by reference, describes a method and an apparatus for conveying materials in bulk by liquid pressure. The method is carried out by an appropriate apparatus and involves loading a material in bulk into a chamber through a loading pipe and then supplying liquid under pressure through a pipe for supplying liquid in the form of a downward annular flow, and discharging the material in bulk in an upward flow through a discharge pipe mounted to extend coaxially with, and inside the pipe for supplying liquid. A zone of recirculation flows of liquid is formed in the chamber by swirling the annular flow to an extent determined by a ratio of the rotational component of velocity to the axial component of velocity at least equal to 0.4. The material in bulk is discharged in the zone of recirculation flows.
Prior patents '009 and '251 both require a pressurized container or vessel that is loaded with solids when it is not under pressure and then sealed and pressurized in order to fluidize and transport solid material in a slurry. It is impossible to install and operate a pressurized container within a wellbore that could be loaded and then sealed in this manner.
U.S. Pat. No. 5,562,159, assigned to Merpro Tortek Limited, incorporated herein by reference, describes a well uplift system to raise material, such as production fluid, from a bore hole that involves pumping water down a pipe to a fluidizing unit (TORE) so that the water activates and entrains the material and carries it up through a discharge conduit to a separator for at least partially separating the fluid and the material. The supply duct in the '159 is connected to a water source at the surface of the well and the discharge duct is connected to a conduit that runs to the surface. However, these features of the '159 invention create a pressure at the bottom of the well (due to the static head of the water column within the supply duct from the surface) that is greater than the pressure within the reservoir in the vast majority of wells that could benefit from this technology. This pressure from the supply duct halts the passing of fluids from the reservoir into the well. In order for the '159 invention, which does not require any artificial lift, to function properly, the pressure in the reservoir would have to be sufficient to lift the fluids to the surface and overcome the static head that would be imposed on the reservoir from the water supply conduit. Since the problem of high sand production is typically not existent in wells with high reservoir pressure, the previous invention has limited commercial applicability for low pressure reservoirs that produce significant quantities of sand that needs to be removed. In addition, there is the added challenge and cost of providing a separate water supply conduit from the surface to the TORE.
U.S. Pat. No. 5,853,266 to Merpro Tortek Limited, also incorporated herein by reference, teaches an improvement to the fluidizing unit of the kind described in the above patents. Specifically, a fluidising unit comprising a supply duct which is arranged to be fed with liquid under pressure, and a discharge duct within the supply duct and projecting beyond the outlet of the supply duct. The end of the supply duct is closable when the fluidizing unit is not in use. A screen is associated with the supply duct, the screen having at least one oblique opening, and being positioned so that liquid passing through the supply duct passes through the or each opening in the screen and is caused to swirl.
Accordingly, there is a need for improved methods and systems, for preventing the accumulation of solids that can stop the flow of fluids into a well, that are not subject to the disadvantages of the prior art. These are now provided by the present invention.